1. Field of the Invention
The present invention relates to a semiconductor device and an information processing system, and for example, to a semiconductor device that determines the transfer speed of a data signal on which different transfer speeds can be set, and an information processing system that carries out communication via the semiconductor device.
2. Description of the Related Art
JP-A-2012-156676, for example, discloses a method in which data signals including long and short pulse widths are received and a signal having a shorter pulse width than a predetermined pulse width is detected and counted, thereby determining the frequency. JP-A-2005-20308 discloses a method in which the clock width of a predetermined number of clocks included in received synchronizing clocks is detected by counting with clocks having higher frequencies than those clocks, then an average value thereof is calculated, and a sampling clock is generated based on the average value.
As information communication devices are becoming increasingly high-speed, for example, transmission rates used for data transmission between LSIs (large scale integrations) within devices are rising, making long-distance transmission particularly difficult. To cope with this problem, a buffer/repeater LSI (referred to, for example, as a signal conditioner) that is inserted in a transmission line of a high-speed serial interface in a device to enable extension of transmission distance is developed. Functions of this LSI to deal with long-distance high-speed transmission may include a receiver to receive signals with small amplitude, a CDR (clock data recovery) to re-time received signals and eliminate jitter, a driver to send out a waveform with large amplitude on which equalization is carried out, and the like. These functions are common techniques that are also used in LSIs such as ASIC (application specific integrated circuit).
Meanwhile, a function of discriminating a transfer speed based on a received data signal is necessary as a signal conditioner-specific function. In order to send and receive a data signal properly via a serial interface, it is desirable to discriminate the transfer speed of a data signal passing through the transmission line and perform waveform equalization or the like corresponding to the transfer speed. As a method for discriminating a transfer speed, for example, it is conceivable to install a logic conforming to serial interface standards and simply read information or the like of the transfer speed included in a communication format defined by the standards. However, such a method has a risk of causing an increase in logic scale and power consumption. Also, there can be circumstances that can only be dealt with by specific serial interface standards.
Thus, a method for discriminating a transfer speed based on a received data signal in the state where there is no protocol analysis based on high-order logic is demanded. As such a method, for example, the methods disclosed in the JP-A-2012-156676 and JP-A-2005-20308 may be employed. However, the method of JP-A-2012-156676 detects the presence or absence of a narrower pulse width than a predetermined pulse width and therefore is suitable for discrimination between two types of transfer speeds. To discriminate three or more types of transfer speeds, for example, measures such as providing plural types of predetermined pulse widths are needed, and this raises concerns about an increase in logic scale and power consumption. The method of JP-A-2005-20308 detects the clock width of synchronizing clocks and therefore needs higher-speed clocks. Thus, the method may be difficult to implement, for example, if the synchronizing clocks themselves are high-speed.